Before installing a plug in an exchanger tube, what should be done to prevent back pressure from building up against the plug?

To prevent back pressure from building up against the plug during installation, it is essential to vent the tube properly. Venting allows any trapped air or residual fluid within the tube to escape, which helps avoid pressure accumulation that could lead to leaks or even damage during the plugging process.

Additionally, performing a fly cut or puncturing ensures that the end of the tube is prepared for a snug fit, helping further to manage any remaining internal pressures. This preparation is crucial in maintaining the integrity of the heat exchanger system and ensuring that the plugging process goes smoothly without causing issues related to pressure buildup.

Other options, such as inspecting and cleaning the tube, while important for maintenance, do not directly address the issue of back pressure. Similarly, replacing the tube completely may not be necessary if a plug can be effectively installed with proper venting techniques, and applying sealant around the plug is also helpful for ensuring a tight fit but does not prevent back pressure prior to installation.